This invention relates to methods and apparatus for use in casting, particularly for use in casting large, irregularly-shaped articles such as engine blocks for internal combustion engines.
Traditional casting methods generally employ a xe2x80x9cgreen sandxe2x80x9d mold which forms the external surfaces of the cast object and the passageways into which the molten iron alloy is poured for direction into the mold cavity. A green sand mold is a mixture of sand, clay and water that has been pressure formed into the mold element. Green sand molds have sufficient thickness so that they provide sufficient structural integrity to contain the molten metal during casting and thereby form the exterior walls of the casting. The structural integrity of the green sand molds, however, is not completely satisfactory and the green sand can easily yield to the pressure that may be exerted by the hands of a workman.
For example, in casting an engine block, a green sand mold is provided with a cavity and preformed cavity portions to position and hold core elements that form the cylinders, coolant passageways and other internal passageways in the cast engine block.
In such casting methods, the core elements that form the internal passageways of the engine block are formed with a high-grade xe2x80x9ccore sandxe2x80x9d mixed with a curing resin so that core elements may be formed by compressing the core sand-curing agent mixture, and curing the resin while compressed to form core elements that have sufficient structural integrity to withstand handling and the forces imposed against their outer surfaces by the molten metal that is poured into the mold cavity. The core sand resin is selected to degrade at temperatures on the order of 300 to 400 degrees Fahrenheit so that the core sand may be removed from the interior of the cylinder block after the molten iron alloy has solidified.
Because of the cost of the core sand, it is desirable that the sand be recovered for further use after it has been removed from the casting. Recovery of the green sand used in the mold is also desirable; however, the large quantities of the green sand-clay mixture can be degraded sufficiently during the casting process that they cannot be economically recycled and must be hauled away from the foundry and dumped. Since the production of such castings is frequently hundreds of thousands of cylinder blocks per year, the cost of handling and disposing of the green sand residue of the casting process imposes a significant unproductive cost in the operation of the foundry. In addition, the core sand frequently becomes mixed with the green sand to such an extent that the core sand cannot be reused in the casting process.
In the invention, a mold and one or more core elements defining the internal passageways of the casting are formed. After the mold and core elements, both of which are preferably formed from resin bonded sand, are assembled, they are placed in a container that is large enough to provide space around the mold-core assembly, and solid particles are is placed in the space between the mold-core assembly and the container to hold the assembled mold and core elements together during pouring of the molten iron alloy into the mold-core assembly and the cooling period during which the molten iron alloy solidifies to form the casting.
In the process of the invention, a plurality of containers are provided and a plurality of mold-core assemblies are provided. The mold-core assemblies preferably comprise core sand mold-forming elements and core sand core-forming elements. The mold-core assemblies are loaded, one after another, into the containers, and the spaces between the mold-core assemblies and the containers are provided with sufficient solid particulate matter to hold the mold-core assemblies together during the casting operations. The containers, with the retained mold-core assemblies, are transported to a pouring station where the mold-core assemblies are filled with molten metal. The poured mold-core assemblies and containers are then allowed to cool until the castings are formed and are transferred after the cooling period to an unloading station where the containers are inverted, the castings are retrieved and the core sand is removed from the interior cavities of the castings. The core sand and the solid particulate material are recovered and can be used in further casting operations.
The solid particulate material is preferably metal particles, for example, spherical steel shot. Using metal particles permits their reclamation by magnetic separation from the core sand. More preferably, the solid particulate matter comprises metal particles formed with the same metal being used to form the castings. Using the casting metal for formation of the solid particulate material permits the reclamation of particulate matter that is fused together by casting metal that does not enter the mold in pouring and that may escape the mold through its interfaces. Such fused casting-metal particles may be re-melted and recast into new individual particles. In addition, such casting-metal particles may be in the form of multi-pointed particles, such as the shape of jacks used in the child""s game.
The assemblage of metal particles around the mold-core assembly helps dissipate the heat from the mold-core assembly, absorbs any casting metal that may escape the mold-core assembly and provides a mold-core assembly support that does not warp in use. Where the metal particles are formed from the same metal being used in the casting operation, metal particles that become fused together by the casting metal may be reclaimed and re-melted (e.g., by xe2x80x9cthrowing them back in the pot.xe2x80x9d)
With the invention, the use of green sand can be eliminated by replacing the green sand molds with a combination of inexpensive reusable containers and reclaimable solid particulate materials, and with mold elements and core elements that are formed by core sand. By eliminating the use of green sand, the cost of the green sand and its clay binders, the problems associated with mixing of the green sand and core sand and their respective binders, and the environmental costs of disposing of the excess green sand are eliminated.
Other features and advantages of this invention will be apparent from the drawings and more detailed description of the invention that follow.